The present invention relates to a catalyst structure for purifying an exhaust gas. Specifically, the present invention relates to a catalyst structure and an apparatus for purifying an exhaust gas comprising platelike catalysts used therein for reducing nitrogen oxides (hereinafter referred to as NOx) in an exhaust gas efficiently with ammonia (NH3).
Nitrogen oxides (NOx) in exhaust gases discharged from power plants, various plants, automobiles, and others are causative agents for photochemical smog and acid rain. As a method for removing NOx, an exhaust gas denitration method by a selective catalytic reduction using ammonia (NH3) or the like as reducing agent has widely been employed with thermal power plants being its center. As denitration catalyst used for such exhaust gas denitration method, a titanium oxide type catalyst containing, for example, titanium dioxide (TiO2) as a main component, and vanadium (V), molybdenum (Mo), or tungsten (W) as active component has been used. Particularly, a catalyst containing vanadium as one of the active components has become a mainstream of current denitration catalysts since the catalyst is not only high in activity, but also small in deterioration due to impurities contained in an exhaust gas and usable at temperatures from a low temperature (Laid-open Japanese Patent Publication No. Sho 50-128681 and others).
As the shape of the catalysts used for such exhaust gas denitration method, honeycomb-like or platelike shape has usually been adopted and various manufacturing methods have been proposed. Among them, catalyst structures obtained by stacking a) many netlike products which are prepared by processing metallic thin plates into metal laths and then spraying molten aluminum thereon or b) many platelike catalysts which are prepared by using woven fabrics or nonwoven fabrics of ceramic fibers as substrate (base plates), applying the catalyst component described above thereon, and then pressing the substrates into elements of a waveform (Laid-open Japanese Patent Publication Nos. Sho 54-79188 and Sho 59-73053 and others) have such excellent characteristics that the draft loss is small and the gas flow passages are hardly clogged with a smoke dust or coal combustion ashes, and thus the catalyst structures are currently used in many denitration apparatuses for exhaust gases from boilers of thermal power plants.
Then, in order to increase the efficiency of exhaust gas denitration apparatuses, attempts to reduce the raw material cost and draft loss by reducing the thickness of catalyst plates have been conducted in many fields in recent years. Also, even in the field wherein exhaust gases discharged from coal burning boilers were objects to be treated and catalysts having a large catalyst pitch (distance between catalysts) were used at a low gas flow speed heretofore, demands for compact denitration apparatuses in which gas flow speed is increased and the catalyst pitch is reduced at the same time to increase denitration efficiency have been increased.
(Although only catalyst structures comprising a plurality of platelike catalysts and gas dispersing members are described hereinafter, it is contemplated that the present invention includes catalyst structures comprising a platelike catalyst and gas dispersing member.)
An object of the present invention is to provide a highly efficient and compact catalyst structure for purifying an exhaust gas and to provide an apparatus for purifying an exhaust gas.
Problems in the prior art described above are solved by the present invention which is summarized as follows:
(1) A catalyst structure, to be disposed in a frame fitting in an exhaust gas flow passage, for purifying an exhaust gas comprising
platelike catalysts having many protruded portions, or mountain portions and valley portions, formed by bending flat platelike catalysts alternately to the reverse direction at a prescribed interval, and
gas dispersing members composed of metallic, ceramic, or glass netlike products having many holes passing from the front surface to the back surface thereof stacked alternately.
(2) The catalyst structure for purifying an exhaust gas recited in paragraph (1) above wherein the platelike catalysts are products produced by applying a catalyst component containing titanium oxide as a main component, and an oxide of vanadium, molybdenum, and/or tungsten added as active component, to meshes of metal laths or glass fiber woven fabrics reinforced with an inorganic bonding agent so that the catalyst component is embedded in the meshes.
(3) The catalyst structure for purifying an exhaust gas recited in paragraph (1) or (2) above wherein the netlike products are metal laths.
(4) The catalyst structure for purifying an exhaust gas recited in paragraph (1) or (2) above wherein the netlike products are glass fiber woven fabrics reinforced by impregnating the fabrics with an inorganic bonding agent.
(5) The catalyst structure for purifying an exhaust gas recited in any one of paragraphs (1) to (4) above wherein a catalyst component is deposited on the surface of the netlike products.
(6) The catalyst structure for purifying an exhaust gas recited in paragraph (5) above wherein the catalyst component is an oxide or oxides of one or more metals selected from the group consisting of titanium, vanadium, molybdenum, and tungsten.
(7) The catalyst structure for purifying an exhaust gas recited in any one of paragraphs (1) to (6) above wherein the protruded portions or mountain portions of the platelike catalysts are formed with their lengthwise direction being inclined relative to one side of the platelike catalysts by a prescribed angle, and a plurality of the platelike catalysts are stacked with the netlike product being interposed therebetween and with the left and right sides of the platelike catalysts being interchanged alternately.
(8) An apparatus for purifying an exhaust gas having a catalyst structure recited in any one of paragraphs (1) to (7) above and disposed in an exhaust gas flow passage.
(9) A catalyst structure to be disposed in a frame fitting in an exhaust gas flow passage for purifying an exhaust gas, comprising
platelike catalysts having many pairs of protruded portions, or mountain portions and valley portions at a prescribed interval formed by bending flat platelike catalysts alternately to reverse direction, and
gas dispersing members prepared by arranging linear, belt-shaped, or rodlike materials of metal, ceramic, or glass in parallel at a prescribed interval stacked alternately.
(10) The catalyst structure for purifying an exhaust gas recited in paragraph (9) above wherein the catalyst plates are products produced by applying a catalyst component containing titanium oxide as a main component, and an oxide of vanadium, molybdenum, and/or tungsten added as active component, to meshes of metal laths or glass fiber woven fabrics reinforced with an inorganic bonding agent so that the catalyst component is embedded in the meshes.
(11) The catalyst structure recited in paragraph (9) above wherein the gas dispersing members are structures prepared by connecting a part or all of the linear, belt-shaped, or rodlike materials.
(12) The catalyst structure recited in any one of paragraphs (9) to (11) above wherein the gas dispersing member is disposed on a line connecting contact points of a protruded portion of one of adjacent catalyst plates with a flat plate portion of the other catalyst plate to be stacked.
(13) The catalyst structure recited in any one of paragraphs (9) to (12) above wherein the gas dispersing members are products reinforced by impregnating the members with an inorganic bonding agent.
(14) The catalyst structure recited in any one of paragraphs (9) to (13) above wherein a catalyst component is deposited on the surface of the gas dispersing members.
(15) The catalyst structure recited in paragraph (14) above wherein the catalyst component to be deposited on the surface of the gas dispersing members is an oxide or oxides of one or more metals selected from the group consisting of titanium, vanadium, molybdenum, and tungsten.
(16) The catalyst structure recited in any one of paragraphs (9) to (15) above wherein the protruded portions or mountain portions of the platelike catalysts are formed with their lengthwise direction being inclined relative to one side of the platelike catalysts by a prescribed angle, and a plurality of the platelike catalysts are stacked with the gas dispersing member being interposed therebetween and with their left and right sides of the platelike catalysts being interchanged alternately.
(17) An apparatus for purifying an exhaust gas having a catalyst structure recited in any one of paragraphs (9) to (16) above and disposed in an exhaust gas flow passage.